DESCRIPTION: The overall objective of the proposed research is to determine the mechanisms responsible for the thermally induced changes that occur in the coefficients of thermal expansion of dental porcelains as a result of multiple firings, slow cooling and post-soldering operations. These changes in porcelain thermal expansion are detrimental and produce cracks in porcelain fused to metal restorations (PFM) either shortly after firing or sometime later. Either event causes additional costs and possibly additional trauma to the patient. There are six Specific Aims. The first is to explain the thermal expansion behavior of porcelains on the basis of leucite and sanidine volume fractions, microcrack densities, an leucite particle surface areas. The second is to determine the effect of localized cooling rate differences on the thermal instability of dental porcelain during multiple firing, cooling, and isothermal anneals. The third is to determine the role of H2O as a glass modifier in dental porcelain and specifically in the crystallization of leucite and sanidine. The fourth is to develop firing schedules for various porcelain-metal systems to minimize the thermally induced microstructural changes that lead to thermal expansion changes.The fifth is to modify porcelains to render them more resistant to thermal expansion changes. The sixth to develop a prototype expert system computer program for solving thermal expansion mismatch problems. Techniques used in pursuit of these aims include quantitative X-Ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, quantitative stereology, and conventional and laser dilatometry.